CHEMICAL AND PHYSIOLOGICAL STUDIES. 187 



in temperature as may at times arise ; but occasionally a con- 

 siderable rise may be observed, more especially in the case of 

 germinating seeds, If the bulb of a delicate thermometer be 

 surrounded in a vessel by some seeds of Pisum sativum, and water 

 added, after a time a rise of some 4° C. will be observed, this 

 being due partly to the absorption of water by the cells of the 

 cotyledons, but mostly to respiration. 



The internal tissues of quickly-growing stems will sometimes 

 indicate a slightly higher temperature than the outer tissues.* 

 In this case, a thermo-electric needle in circuit with a sensitive 

 galvanometer must be used, the needle being so arranged as to 

 be non-polarisable (that is, coated with a substance which is not 

 acted upon by the acid sap). 



In the growing spadix of AroideiP, also, a considerable eleva- 

 tion of temperature has been noted (10° to 12° C.) ; and certain 

 bacteria (Z?. suUilis) also cause a great rise of temperature 

 during growth (c/. firing of hayricks). 



The evolution of radiant energy takes place in some of the 

 lower plants, as in the case of the Bacterium pJiosphoreum, one of 

 the Schizomycetes.f So intense is the radiation in this instance, 

 that pea-seedlings will grow towards a vessel in which a culture 

 of these organisms is growing. Other bacteria, such as those 

 producing the " phosphorescence " of decaying fish, are also 

 capable of evincing light-rays. 



The luminosity in such cases as these is dependent upon the 

 oxidation going on in the cells. 



Differences of electrical potential have been observed to be 

 present between the upper and under surfaces of certain leaves 

 (leaves of Victoria regia, &c.), and it has been shown that if the 

 internal and external tissues of some stems are connected through 

 a circuit in which a sensitive galvanometer is included, a current 

 will flow from the internal to the external parts (Becquerd). 

 Here, also, non-polarisable electrodes are essential. 



In Chapter i., the blaze-reaction mentioned in connection 

 with experiments upon the capacity of germination possessed by 

 seeds, was adduced as evidence of changes in electrical potential 

 produced by oxidative changes of low intensity proceeding in 

 the dormant cytoplasm of the cells composing the seeds ; in fact, 



* See Becquerel, Physiologie Vegetale. 



t See Knowledge and Scientific News, Feb., 1909. 



